1. Field of the Invention
The present invention relates to a planar thin film magnetic head, and more particularly to a magnetic head of a magneto-resistance effect type suitable for a small track width.
There is shown in FIGS. 12 to 14 a conventional thin film magnetic head of a horizontal type or a so-called planar type. FIG. 12 is a perspective view of a magnetic head slider; FIG. 13 is a schematic enlarged sectional view of the thin film magnetic head taken along a direction of a track width; and FIG. 14 is a schematic enlarged perspective view of a magnetic gap of the thin film magnetic head.
Referring to FIG. 12, reference numeral 100 generally designates a magnetic head slider having a base 101. The base 101 is formed with a groove 102 extending in a travelling direction on a surface opposed to a magnetic recording medium (not shown), so that a rail-like ABS (Air Bearing Surface) 81 is formed on the opposite sides of the groove 102. The ABS 81 is formed with a slant surface 104 at a rear end with respect to the travelling direction, so as to effect smooth flying over the magnetic recording medium. Furthermore, a planar thin film magnetic head 90 is formed on the ABS 81 at a front end thereof with respect to the travelling direction.
Referring to FIG. 13, the thin film magnetic head 90 is formed in a recess 101a of the base 101 formed of an insulating material such as silicon. The thin film magnetic head 90 includes a thin film magnetic core 113 formed of a magnetic material such as permalloy, a magnetic gap 118 formed in the thin film magnetic core 113, a conductor layer 114, insulator layers 115 and 75, a coil 116, and a protector layer 117 forming a part of the ABS 81. A through hole 112 is formed through the base 101, so as to form the conductor layer 114 and the insulator layer 115 therein.
As apparent from FIG. 14 showing a gap forming portion of the thin film magnetic core 113 forming the magnetic gap 118, the thin film magnetic core 113 is generally configured such that it is gradually widened in a direction of a track width Tw as it comes away from the magnetic gap 118. Furthermore, the gap forming portion of the thin film magnetic core 113 is formed as a throat portion 119 having a constant width defining the track width Tw. The coil 116 is a thin film coil wound in a plane below the thin film magnetic core 113.
FIG. 17 is a vertical sectional view of a thin film magnetic head of a magneto-resistance effect type (which will be hereinafter referred to as an MR type) as an example of the planar thin film magnetic head 90. Referring to FIG. 17, an MR device 126 as an MR thin film is formed on the base 101, and a thin film magnetic yoke 127 is formed to be connected to opposite ends of the MR device 126. The thin film magnetic yoke 127 is formed at its central portion with a magnetic gap g flush with an ABS 122. A bias conductor 128 for applying a required bias magnetic field to the MR device 126 is formed between the MR device 126 and the thin film magnetic yoke 127 under the magnetic gap g, so that the MR device 126 is operated in a magneto-resistance characteristic area with good linearity and high sensitivity. A non-magnetic protection film 129 is formed on the thin film magnetic yoke 127 except the gap forming portion to constitute a part of the ABS 122.
As shown in FIG. 15, a throat portion 129 of the thin film magnetic yoke 127 forming the magnetic gap g has a width defining the track width Tw. In the case that the track width Tw is relatively large such as about 10 .mu.m or more, a principal magnetic domain 130 becomes a closed magnetic domain structure along a direction of the track width Tw, that is, an axis of easy magnetization can be formed in the direction of the track width Tw. Accordingly, the magnetic head can be operated by rotation of magnetization for a magnetic flux of a signal introduced from the magnetic gap g. As a result, a Barkhausen noise is reduced to provide a linear responsiveness.
However, it has been recently demanded to further increase a recording density, causing the track width Tw to be more reduced. When the track width Tw becomes less than 10 .mu.m, e.g., about 5 .mu.m, the width of the throat portion 129 forming the magnetic gap g becomes small and causes a large influence of shape anisotropy, resulting in a difficulty of orientation of magnetization in the direction of the track width Tw because of an increased static magnetic energy. That is, the axis of easy magnetization is oriented in the direction of the gap length perpendicular to the track width Tw. As a result, a magnetic domain wall in the vicinity of the magnetic gap g in the magnetic yoke 127 irreversibly functions for magnetic flux of a signal introduced from the magnetic gap g upon reproduction, thus exhibiting a non-linear responsiveness. That is, a Barkhausen noise due to movement of the magnetic domain wall is induced in a reproductive waveform, or the magnetic permeability in the vicinity of the magnetic gap g is reduced so that a sufficient reproductive output cannot be obtained.
The above problem occurs not only in the MR type thin film reproducing magnetic head as mentioned above, but also in an electromagnetic induction type planar recording (reproducing) thin film magnetic head having a structure such that a thin-film coil or the like is substantially wound around a magnetic yoke.